1. Field of the Invention
The present invention relates to a variable capacity circuit and a control method of a variable capacity circuit, and more particularly to a variable capacity circuit capable of expanding a variable width of a variable capacity value to a maximum extent without increasing an element area of a variable capacity element even at low supply voltage.
2. Description of the Related Art
Recent mobile communication appliances are demanded to be smaller in size, lower in power consumption, and higher in precision. It is hence required to enhance the characteristic (precision) in wireless parts. Besides, depending on the trend of lower power consumption, the supply voltage is demanded to be much lower (lower Vcc). Especially the characteristic of voltage control oscillation circuit has a serious effect on precision of mobile appliance terminal, and it is required to satisfy both higher precision and lower power consumption at the same time.
FIG. 14 shows a conventional voltage control oscillation circuit 100. The voltage control oscillation circuit 100 comprises an oscillator unit 101, and varactors VA101 and VA102. The oscillator unit 101 is a differential oscillation circuit, and includes oscillation transistors Tr101 and Tr102 and coils L101 and L102. Varactors VA101 and VA102 are variable in capacity, and by varying the capacity by control voltage VT, a voltage control oscillation circuit is composed.